1. Field of the Invention
The present invention relates to a cylinder characteristic variation sensing device that senses a variation among characteristics of respective cylinders of a multi-cylinder internal combustion engine.
2. Description of Related Art
Conventionally, FCCB correction for correcting fuel injection quantities of the respective cylinders is known as correction for smoothing a variation in an injection quantity among cylinders (i.e., an injection quantity variation) caused by individual differences and aging degradation of injectors provided in the respective cylinders and the like in a multi-cylinder internal combustion engine (for example, refer to Patent document 1: JP-A-2001-355500). In the FCCB correction, sensing values of rotation speed of a crankshaft corresponding to combustion strokes of the respective cylinders are extracted from the sensing values of the rotation speed of the crankshaft. A variation among the extracted rotation speeds corresponding to the respective cylinders is regarded as a variation among output torque magnitudes generated by the respective cylinders. The rotation speeds corresponding to the respective cylinders are compared with an average value of the rotation speeds of all the cylinders, and increase/decrease correction (FCCB correction) of the fuel injection quantities of the respective cylinders is performed to smooth the variation in the rotation speed among the cylinders.
The factors of the variation in the output torque among the cylinders include a difference in characteristics of the respective cylinders (a variation in cylinder characteristics) in addition to the above-mentioned variation in the injection quantity among the cylinders. For example, the cylinder characteristic variation includes a variation in various frictions in the cylinders, a variation in compression ratios in the cylinders, a distribution variation of recirculated exhaust gas to the respective cylinders by EGR (exhaust gas recirculation) (shown by a solid line L1 in FIG. 5), a distribution variation of supercharging pressure to the respective cylinders by a supercharger (shown by a broken line L2 in FIG. 5) and the like.
However, in the above-described FCCB correction, even when the injection quantity variation is not caused, the increase/decrease correction of the injection quantity will be performed for the variation in the output torque among the cylinders (or the variation in the rotation speed among the cylinders) resulting from the cylinder characteristic variation. Therefore, the output torque and an emission state of the internal combustion cannot be controlled with high accuracy.